linux-stable/scripts/kallsyms.c
Linus Torvalds 9d82973e03 gcc-10 warnings: fix low-hanging fruit
Due to a bug-report that was compiler-dependent, I updated one of my
machines to gcc-10.  That shows a lot of new warnings.  Happily they
seem to be mostly the valid kind, but it's going to cause a round of
churn for getting rid of them..

This is the really low-hanging fruit of removing a couple of zero-sized
arrays in some core code.  We have had a round of these patches before,
and we'll have many more coming, and there is nothing special about
these except that they were particularly trivial, and triggered more
warnings than most.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-05-04 09:16:37 -07:00

772 lines
17 KiB
C

/* Generate assembler source containing symbol information
*
* Copyright 2002 by Kai Germaschewski
*
* This software may be used and distributed according to the terms
* of the GNU General Public License, incorporated herein by reference.
*
* Usage: nm -n vmlinux | scripts/kallsyms [--all-symbols] > symbols.S
*
* Table compression uses all the unused char codes on the symbols and
* maps these to the most used substrings (tokens). For instance, it might
* map char code 0xF7 to represent "write_" and then in every symbol where
* "write_" appears it can be replaced by 0xF7, saving 5 bytes.
* The used codes themselves are also placed in the table so that the
* decompresion can work without "special cases".
* Applied to kernel symbols, this usually produces a compression ratio
* of about 50%.
*
*/
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <limits.h>
#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof(arr[0]))
#define KSYM_NAME_LEN 128
struct sym_entry {
unsigned long long addr;
unsigned int len;
unsigned int start_pos;
unsigned int percpu_absolute;
unsigned char sym[];
};
struct addr_range {
const char *start_sym, *end_sym;
unsigned long long start, end;
};
static unsigned long long _text;
static unsigned long long relative_base;
static struct addr_range text_ranges[] = {
{ "_stext", "_etext" },
{ "_sinittext", "_einittext" },
};
#define text_range_text (&text_ranges[0])
#define text_range_inittext (&text_ranges[1])
static struct addr_range percpu_range = {
"__per_cpu_start", "__per_cpu_end", -1ULL, 0
};
static struct sym_entry **table;
static unsigned int table_size, table_cnt;
static int all_symbols;
static int absolute_percpu;
static int base_relative;
static int token_profit[0x10000];
/* the table that holds the result of the compression */
static unsigned char best_table[256][2];
static unsigned char best_table_len[256];
static void usage(void)
{
fprintf(stderr, "Usage: kallsyms [--all-symbols] "
"[--base-relative] < in.map > out.S\n");
exit(1);
}
static char *sym_name(const struct sym_entry *s)
{
return (char *)s->sym + 1;
}
static bool is_ignored_symbol(const char *name, char type)
{
static const char * const ignored_symbols[] = {
/*
* Symbols which vary between passes. Passes 1 and 2 must have
* identical symbol lists. The kallsyms_* symbols below are
* only added after pass 1, they would be included in pass 2
* when --all-symbols is specified so exclude them to get a
* stable symbol list.
*/
"kallsyms_addresses",
"kallsyms_offsets",
"kallsyms_relative_base",
"kallsyms_num_syms",
"kallsyms_names",
"kallsyms_markers",
"kallsyms_token_table",
"kallsyms_token_index",
/* Exclude linker generated symbols which vary between passes */
"_SDA_BASE_", /* ppc */
"_SDA2_BASE_", /* ppc */
NULL
};
static const char * const ignored_prefixes[] = {
"$", /* local symbols for ARM, MIPS, etc. */
".LASANPC", /* s390 kasan local symbols */
"__crc_", /* modversions */
"__efistub_", /* arm64 EFI stub namespace */
NULL
};
static const char * const ignored_suffixes[] = {
"_from_arm", /* arm */
"_from_thumb", /* arm */
"_veneer", /* arm */
NULL
};
const char * const *p;
/* Exclude symbols which vary between passes. */
for (p = ignored_symbols; *p; p++)
if (!strcmp(name, *p))
return true;
for (p = ignored_prefixes; *p; p++)
if (!strncmp(name, *p, strlen(*p)))
return true;
for (p = ignored_suffixes; *p; p++) {
int l = strlen(name) - strlen(*p);
if (l >= 0 && !strcmp(name + l, *p))
return true;
}
if (type == 'U' || type == 'u')
return true;
/* exclude debugging symbols */
if (type == 'N' || type == 'n')
return true;
if (toupper(type) == 'A') {
/* Keep these useful absolute symbols */
if (strcmp(name, "__kernel_syscall_via_break") &&
strcmp(name, "__kernel_syscall_via_epc") &&
strcmp(name, "__kernel_sigtramp") &&
strcmp(name, "__gp"))
return true;
}
return false;
}
static void check_symbol_range(const char *sym, unsigned long long addr,
struct addr_range *ranges, int entries)
{
size_t i;
struct addr_range *ar;
for (i = 0; i < entries; ++i) {
ar = &ranges[i];
if (strcmp(sym, ar->start_sym) == 0) {
ar->start = addr;
return;
} else if (strcmp(sym, ar->end_sym) == 0) {
ar->end = addr;
return;
}
}
}
static struct sym_entry *read_symbol(FILE *in)
{
char name[500], type;
unsigned long long addr;
unsigned int len;
struct sym_entry *sym;
int rc;
rc = fscanf(in, "%llx %c %499s\n", &addr, &type, name);
if (rc != 3) {
if (rc != EOF && fgets(name, 500, in) == NULL)
fprintf(stderr, "Read error or end of file.\n");
return NULL;
}
if (strlen(name) >= KSYM_NAME_LEN) {
fprintf(stderr, "Symbol %s too long for kallsyms (%zu >= %d).\n"
"Please increase KSYM_NAME_LEN both in kernel and kallsyms.c\n",
name, strlen(name), KSYM_NAME_LEN);
return NULL;
}
if (strcmp(name, "_text") == 0)
_text = addr;
/* Ignore most absolute/undefined (?) symbols. */
if (is_ignored_symbol(name, type))
return NULL;
check_symbol_range(name, addr, text_ranges, ARRAY_SIZE(text_ranges));
check_symbol_range(name, addr, &percpu_range, 1);
/* include the type field in the symbol name, so that it gets
* compressed together */
len = strlen(name) + 1;
sym = malloc(sizeof(*sym) + len + 1);
if (!sym) {
fprintf(stderr, "kallsyms failure: "
"unable to allocate required amount of memory\n");
exit(EXIT_FAILURE);
}
sym->addr = addr;
sym->len = len;
sym->sym[0] = type;
strcpy(sym_name(sym), name);
sym->percpu_absolute = 0;
return sym;
}
static int symbol_in_range(const struct sym_entry *s,
const struct addr_range *ranges, int entries)
{
size_t i;
const struct addr_range *ar;
for (i = 0; i < entries; ++i) {
ar = &ranges[i];
if (s->addr >= ar->start && s->addr <= ar->end)
return 1;
}
return 0;
}
static int symbol_valid(const struct sym_entry *s)
{
const char *name = sym_name(s);
/* if --all-symbols is not specified, then symbols outside the text
* and inittext sections are discarded */
if (!all_symbols) {
if (symbol_in_range(s, text_ranges,
ARRAY_SIZE(text_ranges)) == 0)
return 0;
/* Corner case. Discard any symbols with the same value as
* _etext _einittext; they can move between pass 1 and 2 when
* the kallsyms data are added. If these symbols move then
* they may get dropped in pass 2, which breaks the kallsyms
* rules.
*/
if ((s->addr == text_range_text->end &&
strcmp(name, text_range_text->end_sym)) ||
(s->addr == text_range_inittext->end &&
strcmp(name, text_range_inittext->end_sym)))
return 0;
}
return 1;
}
/* remove all the invalid symbols from the table */
static void shrink_table(void)
{
unsigned int i, pos;
pos = 0;
for (i = 0; i < table_cnt; i++) {
if (symbol_valid(table[i])) {
if (pos != i)
table[pos] = table[i];
pos++;
} else {
free(table[i]);
}
}
table_cnt = pos;
/* When valid symbol is not registered, exit to error */
if (!table_cnt) {
fprintf(stderr, "No valid symbol.\n");
exit(1);
}
}
static void read_map(FILE *in)
{
struct sym_entry *sym;
while (!feof(in)) {
sym = read_symbol(in);
if (!sym)
continue;
sym->start_pos = table_cnt;
if (table_cnt >= table_size) {
table_size += 10000;
table = realloc(table, sizeof(*table) * table_size);
if (!table) {
fprintf(stderr, "out of memory\n");
exit (1);
}
}
table[table_cnt++] = sym;
}
}
static void output_label(const char *label)
{
printf(".globl %s\n", label);
printf("\tALGN\n");
printf("%s:\n", label);
}
/* Provide proper symbols relocatability by their '_text' relativeness. */
static void output_address(unsigned long long addr)
{
if (_text <= addr)
printf("\tPTR\t_text + %#llx\n", addr - _text);
else
printf("\tPTR\t_text - %#llx\n", _text - addr);
}
/* uncompress a compressed symbol. When this function is called, the best table
* might still be compressed itself, so the function needs to be recursive */
static int expand_symbol(const unsigned char *data, int len, char *result)
{
int c, rlen, total=0;
while (len) {
c = *data;
/* if the table holds a single char that is the same as the one
* we are looking for, then end the search */
if (best_table[c][0]==c && best_table_len[c]==1) {
*result++ = c;
total++;
} else {
/* if not, recurse and expand */
rlen = expand_symbol(best_table[c], best_table_len[c], result);
total += rlen;
result += rlen;
}
data++;
len--;
}
*result=0;
return total;
}
static int symbol_absolute(const struct sym_entry *s)
{
return s->percpu_absolute;
}
static void write_src(void)
{
unsigned int i, k, off;
unsigned int best_idx[256];
unsigned int *markers;
char buf[KSYM_NAME_LEN];
printf("#include <asm/bitsperlong.h>\n");
printf("#if BITS_PER_LONG == 64\n");
printf("#define PTR .quad\n");
printf("#define ALGN .balign 8\n");
printf("#else\n");
printf("#define PTR .long\n");
printf("#define ALGN .balign 4\n");
printf("#endif\n");
printf("\t.section .rodata, \"a\"\n");
if (!base_relative)
output_label("kallsyms_addresses");
else
output_label("kallsyms_offsets");
for (i = 0; i < table_cnt; i++) {
if (base_relative) {
/*
* Use the offset relative to the lowest value
* encountered of all relative symbols, and emit
* non-relocatable fixed offsets that will be fixed
* up at runtime.
*/
long long offset;
int overflow;
if (!absolute_percpu) {
offset = table[i]->addr - relative_base;
overflow = (offset < 0 || offset > UINT_MAX);
} else if (symbol_absolute(table[i])) {
offset = table[i]->addr;
overflow = (offset < 0 || offset > INT_MAX);
} else {
offset = relative_base - table[i]->addr - 1;
overflow = (offset < INT_MIN || offset >= 0);
}
if (overflow) {
fprintf(stderr, "kallsyms failure: "
"%s symbol value %#llx out of range in relative mode\n",
symbol_absolute(table[i]) ? "absolute" : "relative",
table[i]->addr);
exit(EXIT_FAILURE);
}
printf("\t.long\t%#x\n", (int)offset);
} else if (!symbol_absolute(table[i])) {
output_address(table[i]->addr);
} else {
printf("\tPTR\t%#llx\n", table[i]->addr);
}
}
printf("\n");
if (base_relative) {
output_label("kallsyms_relative_base");
output_address(relative_base);
printf("\n");
}
output_label("kallsyms_num_syms");
printf("\t.long\t%u\n", table_cnt);
printf("\n");
/* table of offset markers, that give the offset in the compressed stream
* every 256 symbols */
markers = malloc(sizeof(unsigned int) * ((table_cnt + 255) / 256));
if (!markers) {
fprintf(stderr, "kallsyms failure: "
"unable to allocate required memory\n");
exit(EXIT_FAILURE);
}
output_label("kallsyms_names");
off = 0;
for (i = 0; i < table_cnt; i++) {
if ((i & 0xFF) == 0)
markers[i >> 8] = off;
printf("\t.byte 0x%02x", table[i]->len);
for (k = 0; k < table[i]->len; k++)
printf(", 0x%02x", table[i]->sym[k]);
printf("\n");
off += table[i]->len + 1;
}
printf("\n");
output_label("kallsyms_markers");
for (i = 0; i < ((table_cnt + 255) >> 8); i++)
printf("\t.long\t%u\n", markers[i]);
printf("\n");
free(markers);
output_label("kallsyms_token_table");
off = 0;
for (i = 0; i < 256; i++) {
best_idx[i] = off;
expand_symbol(best_table[i], best_table_len[i], buf);
printf("\t.asciz\t\"%s\"\n", buf);
off += strlen(buf) + 1;
}
printf("\n");
output_label("kallsyms_token_index");
for (i = 0; i < 256; i++)
printf("\t.short\t%d\n", best_idx[i]);
printf("\n");
}
/* table lookup compression functions */
/* count all the possible tokens in a symbol */
static void learn_symbol(const unsigned char *symbol, int len)
{
int i;
for (i = 0; i < len - 1; i++)
token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++;
}
/* decrease the count for all the possible tokens in a symbol */
static void forget_symbol(const unsigned char *symbol, int len)
{
int i;
for (i = 0; i < len - 1; i++)
token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--;
}
/* do the initial token count */
static void build_initial_tok_table(void)
{
unsigned int i;
for (i = 0; i < table_cnt; i++)
learn_symbol(table[i]->sym, table[i]->len);
}
static unsigned char *find_token(unsigned char *str, int len,
const unsigned char *token)
{
int i;
for (i = 0; i < len - 1; i++) {
if (str[i] == token[0] && str[i+1] == token[1])
return &str[i];
}
return NULL;
}
/* replace a given token in all the valid symbols. Use the sampled symbols
* to update the counts */
static void compress_symbols(const unsigned char *str, int idx)
{
unsigned int i, len, size;
unsigned char *p1, *p2;
for (i = 0; i < table_cnt; i++) {
len = table[i]->len;
p1 = table[i]->sym;
/* find the token on the symbol */
p2 = find_token(p1, len, str);
if (!p2) continue;
/* decrease the counts for this symbol's tokens */
forget_symbol(table[i]->sym, len);
size = len;
do {
*p2 = idx;
p2++;
size -= (p2 - p1);
memmove(p2, p2 + 1, size);
p1 = p2;
len--;
if (size < 2) break;
/* find the token on the symbol */
p2 = find_token(p1, size, str);
} while (p2);
table[i]->len = len;
/* increase the counts for this symbol's new tokens */
learn_symbol(table[i]->sym, len);
}
}
/* search the token with the maximum profit */
static int find_best_token(void)
{
int i, best, bestprofit;
bestprofit=-10000;
best = 0;
for (i = 0; i < 0x10000; i++) {
if (token_profit[i] > bestprofit) {
best = i;
bestprofit = token_profit[i];
}
}
return best;
}
/* this is the core of the algorithm: calculate the "best" table */
static void optimize_result(void)
{
int i, best;
/* using the '\0' symbol last allows compress_symbols to use standard
* fast string functions */
for (i = 255; i >= 0; i--) {
/* if this table slot is empty (it is not used by an actual
* original char code */
if (!best_table_len[i]) {
/* find the token with the best profit value */
best = find_best_token();
if (token_profit[best] == 0)
break;
/* place it in the "best" table */
best_table_len[i] = 2;
best_table[i][0] = best & 0xFF;
best_table[i][1] = (best >> 8) & 0xFF;
/* replace this token in all the valid symbols */
compress_symbols(best_table[i], i);
}
}
}
/* start by placing the symbols that are actually used on the table */
static void insert_real_symbols_in_table(void)
{
unsigned int i, j, c;
for (i = 0; i < table_cnt; i++) {
for (j = 0; j < table[i]->len; j++) {
c = table[i]->sym[j];
best_table[c][0]=c;
best_table_len[c]=1;
}
}
}
static void optimize_token_table(void)
{
build_initial_tok_table();
insert_real_symbols_in_table();
optimize_result();
}
/* guess for "linker script provide" symbol */
static int may_be_linker_script_provide_symbol(const struct sym_entry *se)
{
const char *symbol = sym_name(se);
int len = se->len - 1;
if (len < 8)
return 0;
if (symbol[0] != '_' || symbol[1] != '_')
return 0;
/* __start_XXXXX */
if (!memcmp(symbol + 2, "start_", 6))
return 1;
/* __stop_XXXXX */
if (!memcmp(symbol + 2, "stop_", 5))
return 1;
/* __end_XXXXX */
if (!memcmp(symbol + 2, "end_", 4))
return 1;
/* __XXXXX_start */
if (!memcmp(symbol + len - 6, "_start", 6))
return 1;
/* __XXXXX_end */
if (!memcmp(symbol + len - 4, "_end", 4))
return 1;
return 0;
}
static int compare_symbols(const void *a, const void *b)
{
const struct sym_entry *sa = *(const struct sym_entry **)a;
const struct sym_entry *sb = *(const struct sym_entry **)b;
int wa, wb;
/* sort by address first */
if (sa->addr > sb->addr)
return 1;
if (sa->addr < sb->addr)
return -1;
/* sort by "weakness" type */
wa = (sa->sym[0] == 'w') || (sa->sym[0] == 'W');
wb = (sb->sym[0] == 'w') || (sb->sym[0] == 'W');
if (wa != wb)
return wa - wb;
/* sort by "linker script provide" type */
wa = may_be_linker_script_provide_symbol(sa);
wb = may_be_linker_script_provide_symbol(sb);
if (wa != wb)
return wa - wb;
/* sort by the number of prefix underscores */
wa = strspn(sym_name(sa), "_");
wb = strspn(sym_name(sb), "_");
if (wa != wb)
return wa - wb;
/* sort by initial order, so that other symbols are left undisturbed */
return sa->start_pos - sb->start_pos;
}
static void sort_symbols(void)
{
qsort(table, table_cnt, sizeof(table[0]), compare_symbols);
}
static void make_percpus_absolute(void)
{
unsigned int i;
for (i = 0; i < table_cnt; i++)
if (symbol_in_range(table[i], &percpu_range, 1)) {
/*
* Keep the 'A' override for percpu symbols to
* ensure consistent behavior compared to older
* versions of this tool.
*/
table[i]->sym[0] = 'A';
table[i]->percpu_absolute = 1;
}
}
/* find the minimum non-absolute symbol address */
static void record_relative_base(void)
{
unsigned int i;
for (i = 0; i < table_cnt; i++)
if (!symbol_absolute(table[i])) {
/*
* The table is sorted by address.
* Take the first non-absolute symbol value.
*/
relative_base = table[i]->addr;
return;
}
}
int main(int argc, char **argv)
{
if (argc >= 2) {
int i;
for (i = 1; i < argc; i++) {
if(strcmp(argv[i], "--all-symbols") == 0)
all_symbols = 1;
else if (strcmp(argv[i], "--absolute-percpu") == 0)
absolute_percpu = 1;
else if (strcmp(argv[i], "--base-relative") == 0)
base_relative = 1;
else
usage();
}
} else if (argc != 1)
usage();
read_map(stdin);
shrink_table();
if (absolute_percpu)
make_percpus_absolute();
sort_symbols();
if (base_relative)
record_relative_base();
optimize_token_table();
write_src();
return 0;
}